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EUVD-2026-292381

2026-10-08T01:58:16.836843+00:00

EUVD-2026-292381

fkie_cve-2026-41146

2026-10-08T01:58:16.836881+00:00

facil.io is a C micro-framework for web applications. Prior to commit 5128747363055201d3ecf0e29bf0a961703c9fa0, `fio_json_parse` can enter an infinite loop when it encounters a nested JSON value starting with `i` or `I`. The process spins in user space and pegs one CPU core at ~100% instead of returning a parse error. Because `iodine` vendors the same parser code, the issue also affects `iodine` when it parses attacker-controlled JSON. The smallest reproducer I found is `[i`. The quoted-value form that originally exposed the issue, `[""i`, reaches the same bug because the parser tolerates missing commas and then treats the trailing `i` as the start of another value. Commit 5128747363055201d3ecf0e29bf0a961703c9fa0 fixes the issue.

GHSA-2x79-gwq3-vxxm — Uncontrolled resource consumption and loop with unreachable exit condition in facil.io and downstream iodine ruby gem

2026-10-08T01:58:16.836920+00:00

Affected: RubyGems: iodine

### Summary `fio_json_parse` can enter an infinite loop when it encounters a nested JSON value starting with `i` or `I`. The process spins in user space and pegs one CPU core at ~100% instead of returning a parse error. Because `iodine` vendors the same parser code, the issue also affects `iodine` when it parses attacker-controlled JSON.

The smallest reproducer found is `[i`. The quoted-value form that originally exposed the issue, `[""i`, reaches the same bug because the parser tolerates missing commas and then treats the trailing `i` as the start of another value.

### Details The vulnerable logic is in `lib/facil/fiobj/fio_json_parser.h` around the numeral handling block (`0.7.5` / `0.7.6`: lines `434-468`; `master`: lines `434-468` in the current tree as tested).

This parser is reached from real library entry points, not just the header in isolation:

- `facil.io`: `lib/facil/fiobj/fiobj_json.c:377-387` (`fiobj_json2obj`) and `402-411` (`fiobj_hash_update_json`) - `iodine`: `ext/iodine/iodine_json.c:161-177` (`iodine_json_convert`) - `iodine`: `ext/iodine/fiobj_json.c:377-387` and `402-411`

Relevant flow:

1. Inside an array or object, the parser sees `i` or `I` and jumps to the `numeral:` label. 2. It calls `fio_atol((char **)&tmp)`. 3. For a bare `i` / `I`, `fio_atol` consumes zero characters and leaves `tmp == pos`. 4. The current code only falls back to float parsing when `JSON_NUMERAL[*tmp]` is true. 5. `JSON_NUMERAL['i'] == 0`, so the parser incorrectly accepts…